The difference is the length of the ester that is attached to the testosterone. It effects the rate at which the testosterone is released into your system. In Australia, doctors will prescribe Sustanon250. It is a testosterone blend that contains four different types (fast and slow acting), totaling 250mg per ml. Chances are though that you will only find a doctor willing to administer it fortnightly. If you're undergoing TRT then your natural test levels are quite low (obviously). This will give you a boost, but don't expect any great muscle gain. You will only get three ampules per script and it will set you back about $40AUS.